The present invention concerns the tyres and ground contact system of automobiles, in particular the suspension system and more particularly the load distribution on the wheels.
Vehicle tyres are designed for normal operation while pressurised internally by a gas, usually air. However, it can happen that after a pressure loss they have to operate at reduced or even zero pressure. In the case of a conventional tyre, operation at reduced or zero pressure has two main consequences. The first consequence is that the vehicle becomes difficult to steer, uncomfortable, or unstable. The second consequence is irreversible damage to the tyre, which quickly becomes irreparable, sometimes after travelling only a few tens of metres.
Tyres or systems for passenger cars are known, which can operate at reduced or zero pressure to ensure or extend the mobility of the vehicle compared with a conventional tyre, for example after a puncture. These tyres or systems are commonly known as “run flat” because they are able to run when they are flat. One of the concepts that make this possible is based on high rigidity of the sidewalls, which can then work under radial compression and support the tread. This concept is known as “ZP” (Zero Pressure). U.S. Pat. No. 5,968,294 describes such a tyre. Another concept (see U.S. Pat. No. 6,092,575 and U.S. Pat. No. 6,418,992) uses a support located inside the tyre to limit its deflection. The system offered commercially under the name “Pax System” is an example of this concept's implementation. Solutions of those types make it possible to travel a considerable distance after a puncture, for example 200 km, at a limited speed for example of 80 km/h. This enables the user of the vehicle to continue his journey normally and repair the tyre later, whereas a conventional tyre that is punctured must be changed immediately if it is to avoid irreparable damage. Thus, the mobility of the vehicle is greatly extended.